This invention relates to an improved gasket and to a method of making same.
Gaskets, such as automotive head gaskets, are made in a variety of ways. Most frequently they comprise an expansive metallic core and a facing, usually one on each side of the core. The facing material is preferably highly compressed and is mechanically or chemically bonded to the core.
For many years typical preformed gasket facings have comprised asbestos-elastomer mixtures. Usually the facings were separately formed as sheets, which sheets were then laminated to metallic cores, such as tanged cores which mechanically bonded the facings to the core, or to solid cores, to which the facings were chemically bonded, as with suitable adhesives.
Because of the characteristics of asbestos fibers, it was possible to form facings asbestos-elastomer which were suitably dense and low in elastomer content and which, when greater density was required, could be compressed without adversely affecting the facings.
Other processes for forming gasketing material for producing gaskets with metal cores and facings were developed and are typified by the processes and products disclosed in patents such as U.S. Pat. Nos. 3,897,576, 3,922,391, 4,478,887 and 4,520,068. In these patents processes and products are described in which continuous metallic cores are provided, and a facing forming dough, or a facing forming soft material is applied to each side of the core, sometimes with an intermediate adhesive coating on the metallic core to promote securance of the core and facing forming material. The continuously formed gasketing material was then suitable for cutting into lengths, and forming into suitably configured and apertured gaskets, as by die-punching or the like. Some such doughs and soft materials incorporated asbestos fibers and others did not.
Preformed asbestos facings of the types described above were typically formed on paper-making equipment, and were later combined with metallic cores. Facings from doughs and soft materials and formed directly on metallic cores, as described in the patents just referred to, required expensive equipment, and failed to provide the economies and flexibility of manufacture available when facings formed on paper-making type equipment are made and used.
When gasket facings which omit asbestos fibers, and which incorporate primarily other fibers, such as Kevlar (a trademark of E. I. DuPont de Ne Mours) polyaramid fibers, fillers and the requisite relatively low quantities of elastomers or binders, are to be formed, it is frequently not possible to produce sufficiently densified facings, largely because facings of such compositions may not be suitably densified on paper making equipment. Further, after production, they have insufficient structural strength and integrity to permit densification, as via calendering rolls.
Thus, although non-asbestos facing materials are not only desirable, but today are frequently necessary for many gasketing uses, such as for automotive head gasket usage, such facings are frequently not readily usable for such purposes. As such, there remains a void in the art in terms of being able to use many facing materials which are formed of a desired family of ingredients, and which are desirably formed by paper-making processes, and in particular those which may then be effectively combined with non-perforated metallic cores to produce a gasket having suitably densified facings.
Thus, a principal object of the present invention is to provide a process whereby certain classes of facing materials, namely moderate density non-asbestos facing materials formed by a paper-making process may be joined with flat, non-perforated metallic cores, and which may be densified suitably, all without destroying or impairing the facings, and without producing significant waste.